When dispensing liquid in form of drops, e.g., as eye drops, from a tube the size of the drops depends on properties of the liquid such as viscosity and surface tension and on properties of the break-away area of the spout of the tube, i.e., the properties of the area at which the drop breaks away from the liquid flowing to the spout opening. Such properties are in particular the size of the break-away area and its surface tension compared with the surface tension of the liquid. Hence, with the properties of the liquid set the drop size can only be influenced through variations of the break-away area.
Furthermore, typically a drop has to fall to be applied (as, e.g., with drops applied to the eye or skin) or to be further used as with indirect applications.
It is known in the state of the art to provide for different drop sizes by either enlarging or reducing the break-away area at the dispensing end of the spout. For example, the outer diameter of the break-away area is often enlarged for tubes and (also non-squeezable) bottles for dispensing eye drops. However, varying drop sizes by providing break-away areas of different sizes is rather cost-intensive.
If the dispensed drops shall be indirectly used, they are typically dropped onto a spatula or a brush. The spatula or brush, respectively, is then used to apply the liquid. However, the user needs two hands, one hand for squeezing the tube to dispense the liquid, the other hand for holding the spatula or brush.